Cosmology with Cluster Surveys Subha Majumdar Canadian Institute of Theoretical Astrophysics Toronto along with Joe Mohr, Martin White & Jose Diego International

Cosmology with

Cluster Surveys

Subha Majumdar

Canadian Institute of Theoretical Astrophysics Toronto

along with Joe Mohr, Martin White & Jose Diego

International Conference on Gravitation and Cosmology, Kochi, 5th January 2004

Jan 2004Jan 2004 ICGC – 04, KochiICGC – 04, Kochi

Overview Introduction to Galaxy Clusters

Introduction to the Surveys

Studying Dark Energy with Galaxy Cluster Surveys,

the stress in on the eqn. of state “w” of dark energy

(This was the parameter that was not constrained by WMAP+SDSS!

But knowledge of “w” is fundamental to our understanding of dark

energy)

Something new: Self Calibration in cluster surveys

and precision cosmology


Galaxy clusters are the most massive, collapsed structures in the universe. They contain galaxies, hot, ionized gas (107-8K) and dark matter.

In typical structure formation scenarios, low mass clusters emerge in significant numbers at z~2-3

Clusters are good probes, because they are massive and “easy” to detect through their:

What Are Galaxy Clusters?

• X-ray emission• Sunyaev-Zel’dovich Effect• Gravitational lensing

Chandra Image of Zw3158

SZEX-ray

HST


The Basics of SZ Effect

sightofline

pressuregasamplitude

clusteramplitudedependencefreqdistortion

_

)(_


Whats nice about SZE?

1) Ofcourse, the distinct spectral signature2) Measures the total thermal content of the cluster3) More or less redshift independent4) Less susceptible to messy cluster substructure, core physics (prop to density and not density squared as in XRays)


Example: Local Abundance/Mass Function Reiprich & Boehringer 2001

Look at the large error bars!! We want to do much better.

Things will change drastically with future surveys.Especially as a probe of dark energy eqn `of state “w”


Upcoming Cluster SurveysSZ-surveys:

Planck : 2008(?) 7,000/8,000 – 30,000/40,000

SPT : 2005(?) 20,000-30,000

ACT : late 2004 few thousands

APEX : middle 2004 few thousands

X-Ray surveys

DUET : Unsuccesful 20,000-30,000 DUO : very +ve report, late 2004 ~10,000XMM-LSS : 2004+ , ~1000(?)

Cluster surveys will be a thrust area for some time to come!


From observations to detecting clusters: an example

Diego & SM 04


The Cluster Redshift Distribution

Cluster redshift distribution probes:

dN(z)dzd

dV

dzdn z c

H z dA2 1 z 2

dM f M dn M , z dM0

1) volume-redshift relation

2) abundance evolution

Volume Element

Abundance

Mass Selection Function

dN(z)dzd

dV

dzdn z

Volume Abundance

3) cluster structure and evolution.

One can get dN/dz if we can get the redshifts of the detected clusters


Sensitivity of Cluster Redshift Distribution to Dark Energy Equation of State

Increasing w keeping E fixed hasthe following effects

Volume effect Growth EffectFig courtesy Joe Mohr

It decreases volume surveyed

It decreases growthrate of perturbations


Potential for different methods to constrain `w’

Levine, Shultz & White 2002

Complimentary&

Highly Competetive


Dual Nature of Galaxy Clusters It’s critical- for almost any analysis- to keep in mind that clusters

are young objects and yet as a population they exhibit striking regularity

Statistical studies of (x-ray flux limited samples of) galaxy clusters reveal that more than half exhibit merger signatures.

There’s lot of substructures.

Statistical studies of (x-ray flux limited samples of) galaxy clusters reveal regularity

Existence of simple flux-mass relation


Self-Calibration in SZ surveys Two surveys, the South Pole Telescope

Survey and the Planck all sky survey (yielding > 20000 clusters), contain enough information to constrain the interesting cosmological parameters and solve for the structure of galaxy clusters simultaneously!

Assumptions required:1. Hierarchichal structure formation is correct

2. A mass-X-ray luminosity relation exists (or a mass-SZE luminosity relation exists)

3. Crude redshift estimates are available for each cluster detected in the survey

Survey m tot w 8 h n b Norm Slope

Priors flat 0.07 0.050 0.004

Planck 0.017 - 0.075 0.013 0.053 0.041 0.004 24% 0.004

SPT 0.024 - 0.062 0.013 0.047 0.048 0.004 21% 0.005

fx z 4dL2 AM E 2 z

SM & J. Mohr 2003


Self-Calibration : Continued

A Caveat: What if there is “evolution” ??

fx z 4dL2 AM E 2 z 1 z

Everything is lost ! Or is it?

Self Calibration can be regained (by adding complimentary info) ! 1. Need to do follow-up mass estimates of a few clusters 2. Cluster power spectrum, P(k)

Not impressive by themselves, when combined with dN/dz they do wonders


An Example: Planck All Sky Cluster SurveyNclusters ~ 22000

SM & J. Mohr, 2004


How well do we get `w’ ?

Survey On its own

+ P(k) +100 clusters

follow-up

+ Both

SPT 0.18 0.16 0.06 0.035

Planck 0.39 0.10 0.12 0.041

1 error around w=-1, normalized over 9 other parameters

Note: WMAPext gives ~ 0.11

To pin down dark energy we must have cluster surveys + (CMB+SNe)


So what did I say, Upcoming large yield cluster surveys would unveil a new

era of doing cosmology with clusters.

It has the promise to become 4th pillar of precision cosmology

along with CMB, SNe and weak lensing.

As an example, we have shown that these surveys provide us an

opportunity to probe the enigma of dark energy with high precision (the other great way is to do weak lensing tomography)

Most importantly, we’ve seen that even with uncertainties in cluster

physics, `self-calibration’ in these surveys makes clusters an important

tool in precision cosmology ( “w” to few percents, certainly competetive or maybe

even better than what can be done with CMB or SNe alone. )

Documents

Cosmology with Cluster Surveys Subha Majumdar Canadian Institute of Theoretical Astrophysics Toronto along with Joe Mohr, Martin White & Jose Diego International